1) Field of the Invention
The present invention relates to an image forming apparatus for electrophotographic processing, such as a copy machine, a facsimile, and a printer, and more particularly, to an image forming apparatus in which a cleaning of an image carrier is well performed even with use of a toner of a relatively high average roundness.
2) Description of the Related Art
A color image forming apparatus that employs an electrophotographic system is now widely used. Moreover, a high-definition of an image to be printed is desired in association with easy availability of digitalized images. In the study of higher resolution and gradation of images, further conglobation and granulation to finer particle diameter are under research for improvement of a toner that makes latent images visualized in order to form images with the high definition.
For example, several methods are proposed, in which conglobated ground-type toner having a specific particle diameter distribution is obtained (see, for example, Japanese Patent Application Laid-Open Publication No. 1989-112253, Japanese Patent Application Laid-Open Publication No. 1990-284158, Japanese Patent Application Laid-Open Publication No. 1991-181952, and Japanese Patent Application Laid-Open Publication No. 1992-162048), toner conglobated and granulated to smaller particle diameter by suspension polymerization is obtained (see, for example, Japanese Patent Application Laid-Open Publication No. 1993-72808), toner conglobated and granulated to finer particle diameter is obtained by mixing a binding resin and a colorant in a solvent that is not mixable with water, followed by dispersing the mixture in an aqueous solvent in the presence of a dispersion stabilizer (see, for example, Japanese Patent Application Laid-Open Publication No. 1997-15902), and toner conglobated and granulated to smaller particle diameter is obtained by mixing a binding resin containing a partially denatured resin and a colorant in an organic solvent and dispersing the mixture in an aqueous solvent, followed by polyaddition reaction of the denatured resin (see, for example, Japanese Patent Application Laid-Open Publication No. 1999-133668). With the use of the above type of toner, image quality and fluidity are improved.
The toner granulated to finer particle diameter and conglobated is suitable for obtaining images with the high definition because the toner is accurately transferred; however, the conglobated toner is easy to roll down. Therefore, the toner rolls between a cleaning blade and a photosensitive member in a cleaning unit, which makes cleaning difficult. This may result in causes of abnormal images such as background fog.
To cope with the problem, a scheme has been suggested in which a lubricant, such as zinc stearate, is supplied to the surface of a photosensitive member so as to adjust a coefficient of friction on the surface of the photosensitive member, thereby improving cleaning ability. Suggested as an exemplary scheme of supplying a lubricant on the photosensitive member is a method of forming an electrophotographic image using a cleaning member for cleaning, with an elastic rubber blade, a toner remaining on a photosensitive member after transferred to a recording member, wherein the toner contains zinc stearate of equal to or more than 0.01% and equal to or less than 0.5% with respect to the weight of the toner, and the elastic rubber blade is substantially held by a supporting member to be fixed to the cleaning member on a side of a surface on which an image carrier of the cleaning blade is abutted (see, for example, Japanese Patent Application Laid-Open Publication No. 11-184340). However, if zinc stearate is added to the toner, zinc stearate on the image carrier might be non-uniform depending on the state of the image being developed.
Also, another image forming apparatus has been suggested for forming an electrostatic latent image on an image carrier, visualizing the electrostatic latent image as a toner image by using a toner containing a release agent, transferring the toner image on a recording medium directly or via an intermediate transfer member, and fixing the toner image transferred on the recording medium, wherein a lubricant is applied to the image carrier (see, for example, Japanese Patent Application Laid-Open Publication No. 2003-140518).
In the apparatus suggested above, a lubricant applying unit brings a brush-shaped roller into contact with a solid lubricant formed in a block shape, scrapes the solid lubricant by the rotation of the brush-shaped roller, and then, in the downstream of the rotating direction, brings the brush-shaped roller into contact with the surface of the image carrier for applying the lubricant on the surface of the image carrier. However, the solid lubricant has been processed so as not to be prone to lose its shape, and therefore has a hardened surface. Unless this hardened layer is scraped, uniform application onto the surface of the image carrier cannot be achieved. Therefore, when the solid lubricant is first used, an effect of reducing the coefficient of friction on the surface of the image carrier cannot be obtained until the hardened layer is scraped. Thus, it is also difficult to achieve a satisfactory ability of cleaning the image carrier from the beginning.